The polyphenylene ethers and processes for their preparation are known in the art and described in numerous publications including Hay, U.S. Pat. Nos. 3,306,874 and 3,306,875, both of which are hereby incorporated by reference. Other patents which show the preparation of polyphenylene ethers include Price et al., U.S. Pat. No. 3,382,212 and Kobayashi et al., U.S. Pat. No. 3,455,880, which are also incorporated by reference.
The processes most generally used to produce the polyphenylene ethers involve the self-condensation of a monovalent phenol in the presence of an oxygen-containing gas and a catalyst comprising a metal-amine complex.
These processes are run in the presence of an organic solvent and the reaction is usually terminated by removal of the catalyst from the reaction mixture. This has been done by the use of aqueous solutions of acetic acid, sulfuric acid, sodium bisulfate, chelating agents such as glycine, nitrilotriacetic acid and its sodium salts or ethylenediamine tetraacetic acid and its sodium salts. The prior art procedure was based on an extraction of the organic reaction mixture with an aqueous solution, resolving the combined mixture into an aqueous and organic phase, separating the phases and, thereafter, recovering the polymer from the organic phase by various techniques. In any event, the prior art methods most often resulted in catalyst residues being carried over into the polymer due to failure to efficiently separate the viscous polymer solution from the aqueous salt solution. Furthermore, this failure to efficiently separate aqueous-organic phases limited the concentration of polymer in the organic phase by limiting the solution viscosity required to obtain good phase separation. The higher concentration solution of polymer results in a decrease solubility of polymer which makes phase separation difficult.
It has now been found that it is possible to reduce the level of catalyst residue in the polymer by eliminating the prior art steps of phase resolution and phase separation by adding an aqueous solution of a salt of ethylenediamine tetraacetic acid to a reaction mixture of a polyphenylene ether, and thereafter, combining that mixture with an antisolvent for the polyphenylene ether. This procedure reduces the amount of solvent required as polymer solutions with high solids content may be directly contacted with the salt of ethylenediamine tetraacetic acid without dilution.
Accordingly, it is an object of this invention to provide an improved process for the preparation of a polyphenylene ether resin with the aim of obtaining a polyphenylene ether resin with a reduced amount of metallic catalyst residue.
It is also an object of this invention to simplify the preparation of polyphenylene ethers by reducing the number of process steps required to obtain the product, and reducing the amount of solvent required.
It is also an object of this invention to provide a process which permits the removal of metal ion catalyst components from a reaction solution that contains high contents of solids.